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555 Variable Frequency Square Wave Generator
This simple 555 Variable Frequency Square Wave Generator produces a variable frequency output of 2800Hz to 120KHz with this values.
| PARTS LIST | |
| R1 | 2.2kΩ |
| R2 | 4.7kΩ |
| VR1 | 250kΩ |
| C1 | 0.001µF (102) mylar capacitor |
| C2 | 0.01µF (103) mylar capacitor |
| IC1 | NE555 |
The 555 is connected for astable operation. Here the timing resistor is now split two sections, R1 and R2+VR1, with the discharge pin 7 connected to the junction of R1 and R2+VR1. When the power supply connected, the timing capacitor C1 charge towards 2/3 Vcc through R1 and R2+VR1. When the capacitor voltage reaches 2/3 Vcc, the upper comparator triggers the flip-flop and the capacitor start to discharge towards ground R2+VR1. When the discharge reaches 1/3 Vcc, the lower comparator is triggered and a new cycle is started.
The capacitor is then periodically charged and discharged between 2/3 Vcc and 1/3 Vcc respectively. The output state is High during the charging cycle for a time period t1, so that
t1=0.693(R1+R2+VR1)C1
The output state is low during the discharge cycle for a time period t2, given by
t2=0.693(R2+VR1)C1
Thus, the total period charge and discharge is
T=t1+t2
=0.693[R1+2(R2+VR1)]C1 (seconds)
so that the output frequency is given as
f=1/T
=1.443/{[R1+2(R2+VR1)]C1} (You can get frequency in KHz, when R1, R2, VR1 in KΩ and C in µF)
Example:
R1=2.2KΩ
R2+VR1=100KΩ
C1=0.001µF
F=1.443/{[2.2+2(100)]×0.001}
=7.136 KHz
Frequency is adjusted with potentiometer VR1.
To get accurate frequency, you can use regulated power supply.
555 Square Wave Generator
steveteal71
2017/2/5 16:34:29
You are a genuis!